The invention relates to improvements in methods of making, assembling and operating an apparatus which can be utilized to damp vibrations in the power trains of motor vehicles, for example, between the crankshaft or camshaft of an internal combustion engine and the input shaft of a manually shiftable or automated transmission. The invention also relates to improvements in torsional vibration damping apparatus which can be utilized with advantage in the power trains of motor vehicles.
More particularly, the invention relates to improvements in methods of making torsional vibration damping apparatus of the type wherein input and output members are rotatable with and relative to each other about a common axis, wherein the angular movements of the input or output member relative to the other member are opposed by at least one damper, and wherein the input and output members are centered relative to each other by radial and/or axial (thrust) bearings.
Published German patent applications Serial Nos. 35 15 928 A1 and 34 11 092 A1 disclose torsional vibration damping apparatus wherein rotation of coaxial primary and secondary flywheels relative to each other is opposed by a damper employing energy storing devices in the form of coil springs. A journal bearing is provided to center and locate the flywheels relative to each other radially as well as in the direction of their common axis.
It has been found that such centering means which act as radial and simultaneously as axial bearings exhibit a number of drawbacks. One of the reasons is that the parts of the combined radial and axial bearing must be finished and assembled with minimal tolerances which contributes to the cost of the centering means and of the entire torsional vibration damping apparatus. In fact, the tolerances are frequently so narrow that they can be defined as so-called negative tolerances, i.e., the parts which are to rotate and/or move axially relative to each other can carry out the required movements only by overcoming a pronounced resistance to axial and/or angular movement relative to one another. In other words, the frictional resistance which is encountered by the primary and secondary flywheels of a torsional vibration damping apparatus embodying axial and/or radial bearings of the above outlined character operates in parallel with the aforementioned coil springs of the damper.
The combined resistance to rotation of the primary and secondary flywheels in such torsional vibration dampers is often excessive for satisfactory operation of the apparatus in the power trains of numerous types of motor vehicles, especially during certain stages of operation of the vehicles. For example, the combined resistance of the aforediscussed bearings and of the springs of a damper in a torsional vibration damping apparatus is often excessive when the engine is idling, i.e., when the transmission is in neutral gear. Thus, the engine continues to transmit vibratory movements to the input element of the transmission, and this often entails the generation of undesirable noise (such as rattling) in the transmission and/or in certain other constituents of the power train.
Another drawback of presently known and utilized torsional vibration damping apparatus which employ combined axial and radial bearings with parts which are to be assembled with minimal or even negative tolerances is that, due to unavoidable departures from ideal tolerances, the tolerances which actually develop during assembly of a conventional torsional vibration damping apparatus and/or during installation of such apparatus in a power train are highly unpredictable and can vary from apparatus to apparatus or from power train to power train. In other words, the likelihood of ensuring that the quality of the centering action of combined radial and axial bearings in a long (or even short) series of power trains will remain within a desired or prescribed range is rather remote.
On the other hand, attempts to avoid excessively narrow tolerances (or even negative tolerances) and the resulting pronounced friction between the component parts in the centering means (and/or between such component parts and the input and output members of a torsional vibration damping apparatus) by simply increasing the radial tolerances would invariably result in equally unsatisfactory excessive play between neighboring relatively movable parts right from the time of initial assembly of a torsional vibration damping apparatus and its incorporation into a power train. This could result in pronounced wobbling of parts (such as primary and secondary flywheels) in a new apparatus with attendant pronounced or excessive wear and generation of noise within a range (i.e., of an intensity) which is unacceptable to the occupant or occupants of a motor vehicle.